Monday, 20 May 2013

Recessed modular fluorescent lights - Cave Effect

We had an enquiry today from the owner of a building leased out as a hair salon. The landlord had fitted recessed modular 'Cat 2' lights with silver diffusers/reflectors as an improvement. These replaced surface-mounted batten-style fluorescent switch-start T8 fittings.

Thinking the salon owner would be delighted he was shocked when they complained that their customers were just walking past thinking they were closed as it appeared all the lights were switched off. The narrow downward beams of the grid-mounted 4x18W fluorescent lights gave no illumination to the walls or ceiling. It was said to be "like a cave".
Happily the landlord came to Energy At Work for our Patent-Office-protected diffuser kit called GreenCat. This novel idea fits into existing modular lights, saving around 50% of the energy, and includes a dished diffuser-kit which reflects some of the light across the ceiling and upper walls.

Saturday, 11 May 2013

What does CRI mean in lighting?

It means Colour Rendering Index, and is usually given as a number.

Sunlight is usually equated with a perfect colour-rendering (scoring 100). This means in broad terms that a colour-chart would look the way it was intended when viewed in fairly neutral sunlight.
But if you brought that colour-chart under most old industrial lights many of the colours would look much less intense or even shift.
Old-technology fluorescent tubes gave colour rendering as low as CRI=50 but yellow sodium industrial lighting was even worse!

Modern lighting aims at CRI of over 80, which most people feel is acceptable to give fairly realistic interior colours.
However art studios and printing companies may want CRI of over 90 for extreme accuracy.

COB LED array v high-power LEDs

High-power LEDs (single led usually powered at from 1 to 3 Watts)

Creates a small source for the beam, ideal for creating a focussed optical beam using a lens

Flexibility of choices of beam-angles depending on luminaire design

Ability to spread the LEDs widely across a cooling metal circuit-board or heatsink for good heat-reduction to give the LEDs longer life.

To make more light you either need to drive each LED with more power (which is less energy-efficient, eg a 3-Watt LED often gives less than double the light of the same type of LED driven at only 1Watt)  ...or you can add several more LEDs into the light (which costs more and consumes space)
COB array (Many tiny LEDs built into a single unit)
Each tiny LED needs less power as there are many, all creating light and so each LED works very effiiciently
COB LEDs are mounted directly to the printed circuit board and if this has good heat-transfer properties the combination can be good for cooling the LEDs.

As the light comes from a larger area (sometimes more than 4 sq cm) it's difficult to create a sharp, focussed beam
Heat needs to be dissipated from one small 'footprint'. Heat eventually wears-out LEDs so advanced cooling materials/methods are needed if the array's power is over 60 Watts
Beware, some companies who assemble LED hig-bay industrial lights power the LED arrays higher than the manufacturer of the LEDs recommends. This is only bright as a short-term solution as it will wear out the LEDs sooner.
Choosing LED bulbs for restaurants and hotels

We think the main critera are:

How long will it last?

When replacing small spotlights such as 50W GU10/MR16 we suggest using LED bulbs of 4 or 5Watts because LEDs create heat, yet hate running hot, so a higher power bulb (eg 9Watts) can't shed enough heat to give a long life.
Replacing standard round '60-watt light-bulbs' (called GLS bulbs) we find 7Watts is enough but suggeest using LEDs up to 10Watts but only if the heatsink is large and well-finned (surface-area is all-important).

Will it fit?
Some spotlight fittings have tight shapes, so it's vital to test-fit one sample to make sure it will fit.
Also bear in mind that if the bulb fits into the light-fitting with no air-gap, the heatsink won't remove as much heat into the air, so the LEDs will be hotter while running - that means you might reduce the life-expectancy or decide to use LEDs of a lower power in Watts.

Will it be bright enough?
We find our 5Watt spotlights are enough to match the ground-level light of most mains GU10 bulbs.
LED spotlights were quite inefficient when using just one LED that needed a lot of electrical power. Moving to three or four LEDs per bulb worked well as it allowed carefully designed optical lenses to be fitted, and we sell a lot of these due to the quality of the light-beam.
LED-bulb brightness/efficiency has taken a new leap now it's possible to fit arrays of many LEDs into a small space. Each tiny LED needs to be driven less hard and gives more light per unit of power.
Our 7Watt 'standard light-bulb' shaped LED-bulbs are a match for 11Watt CFL bulbs or 60Watt standard 'incandescent' tungsten bulbs.
Look for quoted 'lumens' but also test the light and look at the beam and colour, as there are many different qualities and beams given by LEDs so the wattage alone doesn't tell you how bright it will be.

Will the beam be wide enough to cover tables and avoid patchy-lighting?

We have tested many lenses over the years and only found a few that are wide enough yest still bright enough to make a diference. Many cheap LED bulbs with inefficient LEDs fake brightness by producing a very narrow beam.  If a cheap LED bulb can only illuminate a table 2ft wide, but another bulb illuminates a table 4ft wide, and each registers the same brightenss on that table, the bulb with the wider beam would be producing several times as much light!
Inevitbly if you bought the first type of bulb becuase singly they're cheaper, you would probably have to fit three or four times as many of them to cover the restaurant or bar.

Will the beam-colour enhance our ambience?
Choose whether you want to create a fresh modern, clean-and-classic, or antique ambiance. We can create bulbs for you which give a beam in colours including very-warm, standard warm, neutral (and even cool-daylight but we don't recommend this very often).
Always test a sample in-situ.

How much to pay?The price of LEDs has fallen gradually but as new versions are developed that give more light for less energy there is now a wide choice - for example you can pay anything from £1 to £30 for a dicroic-style 50mm LED spotlight. While some of the price-variation is just profiteering by a few 'brands' a lighting specialist can look at your lighting needs and recommend LED lighting at a price-level that will give you the performance and lighting-effect you need.
How can I tell if LEDs in a light, tube or bulb will last a long time?
So the shop claims an LED light will last over ten years, or maybe 50,000 hours plus?
How can you tell how long LEDs are likely to last?
LEDs are not like modern fluorescent lighting - heat is their enemy.

You can be the detective.

You can start by thinking like of an LED like a living creature - they get warm when they work hard (making light),   ...if they get TOO hot they'll get worn-out soon.
Remember, LEDs visibly decrease in brightness as they deteriorate, so their 'life expectancy' is not the full story...

Look to see if there's anything else near the LEDs that will make me the LEDs even hotter.
Commercial LED-lights need a transformer to convert mains-power to the voltage LEDs can use, and that creates heat too.
Where is the transformer?
Is it in the same small 'space' as the LEDs making the LEDs hotter?

If the driver and transformer were inside this tube, the LEDs could overheat and fail soon
...or is it in a separate housing that can release heat to the air, connected by a wire to the LED-unit?
The same LEDs can last longer if the transformer is kept separate so there is less heat around them.
Most types of LED lights (including LED-tubes) are available with independent transformers if you look for the right supplier.

LED Light with large finned heatsink, and independent matched driver to keep mains heat away from LEDs (rear)
See how the designer plans to allow the LEDs to stay cool.EG. Are the LEDs mounted on a metal finned 'heatskink' which draws the heat from the LEDs and allows air to pass through the fins drawing the heat away?
There are good and bad heatsinks of course - the more fins and surface-area usually the better. Also LEDs of over 70 Watts benefit from other ways to conduct heat than just aluminium, starting with copper-pillars within the aluminium to bring the heat away from the LED faster.

How high is the total LED power?
As you can imagine, more power = more heat, so a single 1-Watt LED might survive for years with just a 1 cubic cm aluminium heatsink, but with a small heatsink a single 150W LED-source (eg industrial LED high-bay lighting) definately won't - the best examples of these use other cooling methods such as condensing or liquid-cooled systems.
As this is expensive, another solution is to fit more lights but reduce the power of each.  Two 75Watt LED lights with a single LED chip or "array" on a basic 'finned' heatsinks are likely to last longer on average than 150Watt light of similar design.

Instead of a single powerful LED light-source, some LED lights deal with the cooling challenge by using many low-powered LEDs spread across a much wider cooling surface. For example we make
LED light-fittings which replace ageing compact '2D' circular ceiling-lights. These have a metal body, with up to 50 small LEDs mounted across it:
Multiple LEDs on large heatsink for cooling=long life
 Cover should not prevent air getting to metal body

Would buying big-brand lighting assure long life?

Unfortunately, many 'high-street' names now make LED lights, but a lot are built down to a price, aiming to leave profit for their big infrastructure and advertising budget, and aimed at the domestic market where it's expected the bulbs won't be used many hours a week (maybe three hours a day in a bathroom compared to 24/7 in a hotel washroom).
Next time you're in a supermarket or DIY-shop spot the 'big brand' LED-bulbs or ceiling-lights with no heatsink at all, just moulded plastic which has almost no cooling ability but costs a fraction of what graded aluminium does??

 Professional-use 'long-life' LED bulb with deep finned aluminium heatsink

So it's usually better to find an expereinced supplier who already works with the sector you're in and understands the impacts created by the way you'll be using the bulbs. Picking a supplier who's worked under many Carbon Trust or Salix funded commercial schemes over many years is a good reassurance.
What does 'High Frequency' or 'HF' mean in lighting, tubes or bulbs?

It means when you look at the light you don't see flicker caused by the power-supply into your building.

With old-style fluorescent lighting and cheap LED-bulbs the mains 'AC' or 'Alternating Current' flicker-rate can affect your concentration and possibly even your health.

Even though the mains-power in the UK is flickering/alternating at up to 60-times per second, in lighting this is believed to be slow enough for your eyes and brain to notice and try to compensate for.
When you look at bright sun your eyes quickly adjust to reduce the amount of light entering, but if you try to do that 60-times a second some people experience headaches or eye-strain, and nobody likes it much.

LEDs and fluorescent tubes aren't just connected directly to the mains. Fluorescent and LED lighting relies on an attached controller that takes electrical power and converts it into the right spec of electrical energy to run the light-source. In fluorescent lighting this is usually still called the 'ballast'. In LED lights it's called the 'driver'.
However old fluorescent lights which had 'starters' make the tube flicker with the mains 'AC' rate.
What's more shocking is that some cheap LED-bulbs don't have components to prevent this mains 'AC' flicker. One health-related UK government department we supply tested LED-lights from another (previous) supplier and found they flicker too slow for good health of the staff working below them. Ours passed their test because we made sure they flickered so fast that the human eye/brain is not aware or affected (our LED downlights flickered approx 100,000 time each second!).